1. Field of the Invention
The present invention relates generally to memory modules, and in particular a memory module that connects circuit boards via an area array.
2. Description of Related Art
The semiconductor industry is constantly producing smaller and more complex semiconductors, sometimes called integrated circuits or chips. This trend has brought about the need for smaller semiconductor chip packages with smaller footprints, higher lead counts, and better electrical and thermal performance, while at the same time meeting accepted reliability standards.
In complex microelectronic devices, different semiconductor components connect to one another through various types of connectors. The reliability of these connectors is critical to the proper functioning of these microelectronic devices. However, as such microelectronic devices become smaller and more complex, the density of input and output electrical contacts on the devices increases. This means that the pitch or space between such contacts is continually decreasing. For example, semiconductor chips today contain up to 2000 pins per square inch, requiring a pitch as small as 0.003 inches.
In addition, as the number of pins on semiconductor chips increases, the number of contacts on the circuit boards carrying these semiconductor chips also increases. Therefore, today""s circuit board connectors need to have a high density of contacts with a small pitch. However, it becomes increasingly more difficult for reliable contact to be made, as pitch decreases.
There are common situations where it is desirable to connect two circuit boards to one another. For example, it may be desirable to couple a circuit board of a memory module to a target board, such as a motherboard. Such memory modules include Dual In-line Memory Modules (DIMMs), Single In-line Memory Modules (SIMMs), RAMBUS In-line Memory Modules (RIMMs), or the like. Typically, these memory modules connect to a target board via a male card edge connector that mates with a female card edge connector or socket on the target board.
FIG. 1A is a front view of such a prior art memory module 100 including a male card edge connector 103 and its corresponding female card edge connector or socket 104 on a target board 106. The edge card connector 103 includes a set of pins or contact pads 102 located along an edge of a memory module 100. These contact pads 102 electrically engage with corresponding contacts in the socket 104, which is soldered onto a target board 106. Each memory module 100 typically includes of a number of memory chips 101.
FIG. 1B is a side view of the prior art memory module 100 shown in FIG. 1A. A disadvantage of such a male card edge connector 103 is that the number of contact pads 102 that can be placed along the edge of the memory module 100 is very limited. As the demand for memory capacity increases, so does the number of semiconductor chips 101 required per memory module 100. This increase in the number of semiconductor chips 101 leads to an increase in the number and density of contact pads 102 on the memory modules 100.
As the density of the contact pads 102 increases, it becomes more difficult to provide reliable electrical contact due to inherent surface irregularities on the circuit board and contact pads. These surface irregularities may prevent some of the contact pads from making contact with corresponding contacts in the socket 104. Additionally, interference, such as electrical fields, generated between contact pads limit how close contact pads may be placed to one another. Additionally, these female card edge type connectors or sockets occupy a relatively large footprint on the target board and also substantially increasing the height of the target board. In light of the above, card edge connectors are becoming increasingly undesirable in today""s ever shrinking microelectronics devices.
Another way of packaging microelectronic devices, in order to achieve higher counts of input and output electrical contacts, is by employing area arrays. An area array 202, shown in FIG. 2A, comprises a group of contact pads 200 arranged in a matrix on a circuit board 201. Area arrays 202 allow connectors to have more contacts spaced sufficiently far away from one another to avoid the drawbacks associated with card edge connectors.
Connectors such as DELPHI CONNECTION SYSTEMS"" GOLD DOT connector utilize area arrays to connect circuit boards to each other. FIG. 2B shows a side view and FIG. 2C shows a front view of such a prior art GOLD DOT connector 205, as viewed along arrow 2C of FIG. 2B. The GOLD DOT connector 205 comprises two sets of gold plated pins or xe2x80x9cdotsxe2x80x9d 204(1) and 204(2) contained on a flexible circuit board 203. The flexible circuit board is usually shaped by mounting on a block 212 or a bracket so as to create a rigid connection between a circuit board 208 and a target board 206. Pins 204(1) to 204(2) make contact with the contact pads 210(1) and 210(2) located in area arrays on the circuit board 208 and the target board 206, respectively. The boards 206 and 208 are kept in contact with the GOLD DOT connector 205 by clamping each of the boards 206 and 208 to the GOLD DOT connector using two separate clamps (not shown).
A disadvantage of this type of connector is the high number of contact xe2x80x9cdotsxe2x80x9d that comprise the two sets of pins 204(1) and 204(2). The additional contact points increase the likelihood of inadequate electrical connections being formed. Also, because GOLD DOTs currently cost up to $0.02/dot, the GOLD DOT connectors make large arrays prohibitively expensive. Another drawback of the GOLD DOT connector is the use of two separate clamps, which increases the cost and size of the connector arrangement.
In view of the foregoing, it would be highly desirable to provide an electrical connector that addresses the abovementioned drawbacks, while providing connector that is reliable at a low associated cost per electrical connector.